Asian breeders claim pellets make the spots gain pigment. Same way that quality pellets can make FH and other fishes gain reddish color they can make pure white spots turn brownish.
Just a claim by some breeders. Some refuse to feed pellets.
That's because those Asian breeders were most likely feeding Asian made fish food full of synthetic color enhancers such as Carophyll Pink, a synthetic form of astaxanthin. Unlike foods that use synthetic gimmicks (or hormones) for color enhancement, a high quality pellet will not enhance a fish beyond its natural coloration.
I've personally seen numerous BD's fed quality pellet food (some exclusively fed pellets) and the spots were all as white as snow.